Include transcode hw requested and transcode hw full pipeline

[ammmze]

Would you be open to a PR to add transcodeHwRequested and transcodeHwFullPipeline labels to the plex_transcode_sessions_active_count metric? I've had a few times where something has gone awry in my system and hardware transcoding stopped working and so I'd like to use this to set up some prometheus alerts when hardware transcoding stopped working.

[othalla]

Hey,
I'll have a look soon!